Municipal utilities usually bury their mains under public rights of way, such as streets, at spaced intervals throughout the system. Normally open shut-off valves are incorporated for the purpose of isolating main breaks so they can be repaired or new connections established.
The shut-off valves are frequently buried several feet beneath the street and access pipes are provided which extend upwardly from the valve to near street level. The access pipe provides a passage for a tool which can be manipulated from street level to actuate the valve.
A cover assembly with a removable lid is usually incorporated in the street pavement to prevent debris from entering the access pipe.
It has been customary to fabricate both the lid and the lid support of the cover assembly from cast iron. These are of low cost and durable. Iron castings, however, are notorious for dimensional variations from one casting to the next. Consequently, it frequently is the case that there is a poor fit between the lid and the lid support.
Nevertheless, cast iron has remained the material of choice because it is strong and capable of withstanding the rigors to which a pavement-mounted assembly is subjected.
It has more recently been recognized that quality cover assembly components can be modeled from light-weight synthetic polymeric material. U.S. Pat. No. 4,048,766, granted Sep. 20, 1977, to P. H. Dantzer et al. for "Closure Lid Assembly for Protective Housings" suggests the components be formed by a structural foam molding process.
The light weight of the lid in the Dantzer et al. assembly requires that special retaining means and a locking system be provided in the design to prevent the lid from being accidentally dislodged.
It is also known to provide sealing flaps on the periphery of a lid to seal the junction between the lid and it's support structure. An example of this technique is illustrated in U.S. Pat. No. 5,404,676, granted Apr. 11, 1995, to M. Devlin for "Watertight Pit Cover".
There continues to be a need for an access cover assembly which can be easily molded from polymeric material and which will perform reliably in service.